COMPLETE SUBSTITUTION OF DIETARY WHEAT BRAN WITH DUCKWEED LEMNA SPECIES SUPPLEMENTED WITH EXOGENOUS DIGESTIVE ENZYMES FOR FRESHWATER PRAWN, MACROBRACHIUM ROSENBERGII (DE MAN 1879) POST LARVAE
Introduction
Regarding to the value of duckweed as an aquatic crop used either as a supplementary food dried ingredient for addition into cattle, poultry, fish, crayfish and shrimp ration (Davis and Arnold, 2000). Furthermore, duckweed leaves contain little fibre and little to no indigestible material even for monogastric animals (Chaturvedi et al., 2003). This contrasts with the compositions of many crops such as soybeans, rice and maize, approximately 50% of whose biomass comprises residues high in fibre and low in digestibility. However, lower accepted and effectiveness of fresh plant as a feed ingredient for marine and freshwater species was recorded due to the lack of exogenous enzymes. Enzymes provide additional powerful tools that enhance the nutritional value of shrimp feeds. The addition of enzymes in feed can minimize the anti-nutritional effects and effluent pollution, and reduce both feed cost and the excretion of nutrients into the environment (Felix and Selvaraj, 2004).
The present study was conducted to evaluate the effect of dietary duckweed, Lemna spp. levels with or without exogenous enzymes mixture (Pepsin, Amylose, Lipase, Protase and Hemicellulose) supplementation as replacer of dietary wheat bran for freshwater prawn, Macrobrachium rosenbergii post-larval.
Materials and methods
Prior to trial, the prawns were acclimated to experimental condition for two weeks in a concrete pond (8x4x1 m). During this period, PLs were fed daily a control diet (35% CP). At the end of the acclimation period, a 30 day-old with an average weight of 0.2 ± 0.02 g of M. rosenbergii PLs were stocked into five cement ponds. Each pond (6 m3) was divided into three equal pens by nets (2 m3). Experiments were carried out in triplicates for each treatment with stocking density of 84 PL/m2.
Five isonitrogenous (35% CP) and isocaloric (19 MJ GE kg-1) diets were formulated. Control diet was not supplemented either with Lemina spp. or exogenous enzymes mixture (Pepsin, Amylose, Lipase, Protase and Hemicellulose) which classified as positive control (T1). Negative control diet (T2), was formulated by replaced all dietary wheat bran with Lemina spp. without exogenous enzymes mixture supplementation. Diets T3, T4 and T5, were formulated similar to the negative control diet and supplemented with three different exogenous enzymes mixture of Pepsin, Amylose, Lipase, Protase and Hemicellulose. The growth indices, feed utilization, and chemical proximate compositions of M. rosenbergii PLs were calculated over 84 experimental days.
Results and Discussion
The data revealed that addition of exogenous enzyme mixture into diets T2, T3, T4 and T5 exhibited greater M. rosenbergii PLs growth and feed utilization in terms final body weight, weight gain, specific growth rate and feed conversion ratio compared to the control diet (T1) and negative control diet (Table 1). The same trend was observed for the highest protein contents of M. rosenbergii PLs while the opposite trend was recorded for the whole body lipid content for prawn fed the diets supplemented with both Lemna and exogenous digestive enzyme (T3, T4 and T5). The best FCR was observed for prawn fed diet T3.
The results indicate that the diet in which 80% of the wheat bran is replaced by duckweed, Lemna spp. With exogenous enzymes mixture supplementation up to 300 mg/kg pepsin, 1500 unit/kg Amylose, 2400 μg/kg lipase, 1500 unit/kg protease and 120 mg/kg hemicellulose yields higher growth and production, and is as cost effective, as the control diet.
References
Chaturvedi, K.M.M., Langote, D.S. and Asolekar, R.S. 2003. Duckweed-fed fisheries for treatment of low strength community waste water. WWWTM Newsletter-Asian Insttitute of Technology, India.
Davis, D.A. and Arnold, C.R. 2000. Replacement of fish meal in practical diets for the Pacific white shrimp, Litopenaeus vannamei. Aquaculture, 185: 291-298.
Felix, N. and S. Selvaraj, 2004. Enzyme for sustainable aquaculture. Aquaculture Asia Magazine, 1: 5-6.
